Conventionally in the IC manufacturing process, different cleaning processes are required for the silicon wafers and during the cleaning processes, different chemical liquids may be used. For example, the chemical liquid ST250 is generally used in a cleaning apparatus for cleaning copper interconnections; the chemical liquids such as ammonia, oxyful, hydrofluoric acid, etc are generally used in a cleaning apparatus for cleaning polished wafers. In addition, the purity of the chemical liquids is highly required. In the cleaning processes, the different chemical liquids are usually transported to each machine of the equipment through chemical liquid storage devices.
The Chinese patent No.201857044U discloses a conventional chemical liquid storage device. As shown in FIG. 1, the conventional liquid storage device generally comprises a liquid storage tank 110, a liquid intake tube 120, a liquid discharge tube 130, a gas intake tube 140, a pressure relief tube 150, a pressure relief valve 151 disposed on the pressure relief tube 150, a vacuum breaking tube 160, and a vacuum breaking valve 161 disposed on the vacuum breaking tube 160; the liquid intake tube 120, the liquid discharge tube 130 and the gas intake tube 140 are all connected with the liquid storage tank 110.
Referring to FIG. 2, the patent mentioned above also describes an improved liquid storage device 200 comprising a liquid storage tank 210, a liquid intake tube 220, a liquid discharge tube 230, a gas intake tube 240 and a liquid pressure maintaining device; the liquid intake tube 220, the liquid discharge tube 230, and the gas intake tube 240 are all connected with the liquid storage tank 210; the liquid pressure maintaining device comprises an overflow tube 250 and a liquid seal container 260 with liquid stored therein; one end of the overflow tube 250 is connected with the liquid storage tank 210, and the other end extends into the liquid in the liquid seal container 260. The liquid seal container 260 is an opening container comprising a side wall 261 and a bottom wall 262 connected with the side wall 261. The liquid pressure maintaining device also comprises a liquid infusion tube 270 and a liquid drain tube 280, the liquid infusion tube 270 and the liquid drain tube 280 are both connected with the side wall 261 of the liquid seal container 260. A first valve 221 is arranged on the liquid intake tube 220 for controlling the on-off of the liquid intake tube 220; a second valve 231 is arranged on the liquid discharge tube 230; and a third valve 241 is arranged on the gas intake tube 240.
The main difference between the two liquid storage devices mentioned above is the operation way of the device under a gas overpressure condition and a gas underpressure condition. The liquid storage device illustrated in FIG. 1 utilizes the pressure relief valve and the vacuum breaking valve to control the pressure in the liquid storage tank. However, since the pressure relief valve and the vacuum breaking valve are interlock mechanisms and easy to lose mechanical sensitivity after being used for a certain time, the pressure in the storage tank may become unstable which may result in the damage of the tank and affect the whole manufacturing process. The liquid storage device illustrated in FIG. 2 utilizes the overflow tube and the liquid seal container to maintain a stable pressure in the liquid storage tank. However, the depth of the overflow tube extending into the liquid seal container is required to be adjusted to prevent the liquid in the liquid seal container flowing back into the liquid storage tank. Moreover, since the liquid in the liquid seal container is generally de-ionized water which encourages the growth of bacterial, the control of the quality of the de-ionized water in the liquid seal container is required and has to be taken into consideration during the application of the de-ionized water.